1. Field
Various embodiments of the present disclosure pertain generally to shock absorbers for vehicles. Specifically, the disclosure pertains to position dependent, internal bypass shock absorbers that allow for independent adjustment of shock absorber resistance in both compression and rebound phases.
2. Background
Generally, suspension springs of a vehicle support the weight of the vehicle and its load, and absorb road shocks. Shock absorbers help control or dampen spring action to avoid spring oscillation and assist in maintaining control of the vehicle, and as a result, are also referred to as “dampers.” When a vehicle moves over a bump in the road, the wheel accordingly responds by moving up with the bump, and then back down after having passed the bump. As the vehicle moves over the bump, the spring and shock absorber compress since the wheel moves up toward the “sprung weight” of the vehicle in a phase referred to as “compression.” After passing the bump, the spring and shock absorber extend out in the opposite direction in a phase referred to as “rebound.” A correctly designed spring and shock absorber system goes through a small degree of oscillation in return to its steady state condition.
Ideally, the shock absorber will not only control oscillation, but also prevent the spring from achieving either full compression or full extension. Full compression indicates that the vehicle's suspension system is “bottomed out.” Bottoming out may damage the spring and/or shock absorber. Full extension means that the vehicle's suspension system is “floating,” and possibly no longer in contact with the road. Thus, a well designed spring/shock absorber system allows the vehicle chassis to remain relatively steady, and keeps the tires in contact with the ground despite bumps or holes in the road, and/or forces caused by cornering or changes in the vehicle's speed.
In high performance applications, such as off-road applications, and/or off-road racing, the springs and shock absorbers are considered one of the more important tunable systems on the vehicle, and one that can greatly affect the vehicle's handling characteristics. Indeed, adjusting the shock absorber characteristics can dramatically affect the way the off-road vehicle performs when it drives over uneven terrain, turns a corner, accelerates, and/or brakes.
Most shock absorbers include an oil-filled cylinder or tube in which a single piston moves up and down in response to movement of the wheel relative to the vehicle chassis. The piston typically divides the cylinder into upper and lower fluid chambers. The movement of the piston forces oil or hydraulic fluid in the cylinder to flow through small fluid passages or channels in the piston. The channels in the piston may be restricted by spring-loaded check valves or deflection discs that deflect under pressure. The resulting fluid friction limits both compression and rebound. The more easily the fluid flows through the channels, the softer the ride. In contrast, smaller channels and stiffer check valves or deflection discs, have greater restriction and provide a stiffer ride. Thus, varying the size of the channels, or the stiffness of the valves or deflection discs, alters the rebound and compression characteristics of the spring/damper system, and changes the ride characteristics of the vehicle. For high performance applications, such adjustability is greatly desired, particularly if the rebound and compression settings can be independently changed in a variety of ways.
Prior art shock absorbers typically provide limited means by which the rebound and compression characteristics can be adjusted. For example, a shock absorber with a single piston will typically provide limited internal bypass chambers for fluid flow. Accordingly, the number and location of the check valves and/or deflection discs that fit over the orifices of these internal bypass chambers are inherently limited.
For example, FIGS. 1 and 2 illustrate sectional views of a shock absorber found in the prior art. The shock absorber 100 comprises a fluid filled cylindrical housing 102 that slidably retains a piston 104. The piston 104 is coupled to one end of a piston rod 106. The piston 104 divides the housing 102 into an upper fluid chamber 108 and a lower fluid chamber 110. An opposing end (not shown) of the piston rod 106 extends out beyond the housing 102. During compression, the piston rod 106 is pushed/forced within the housing 102 in a direction toward the top end 112 of the shock absorber 100. During rebound, the piston rod 106 is pulled/forced within the housing 102 in a direction away from the top end 112 of the shock absorber 100.
FIG. 1 depicts the shock absorber 100 undergoing compression since the piston rod 106 and piston 104 are moving in a direction toward the top end 112 of the shock 100 (as indicated by the large, single arrow at the bottom of FIG. 1). During compression, fluid from the upper fluid chamber 108 is forced past channels in the piston 104 and flows into the lower fluid chamber 110 (as indicated by the smaller curved arrows). During rebound, fluid from the lower fluid chamber 110 is forced past different channels in the piston 104 and flows into the upper fluid chamber 108. The force required to move the fluid between the two fluid chambers 108, 110 gives the shock absorber, in part, its compression and rebound resistance.
FIG. 2 illustrates a detailed view of components that may comprise the piston 104. For example, the piston 104 may include a plurality of compression channels 202 that are sized and located so that they can be covered by stacks of washers or deflection discs forming valves on each side of the piston 104. Specifically, the compression channels 202 have entrance openings 204 and exit openings 206 that allow for the flow of fluid from the upper fluid chamber 108 to the lower fluid chamber 110. A compression valve deflection disc stack 208 (also referred to herein as a “compression valve stack”) sits flush against the exit openings 206. The compression valve stack 208 is comprised of a plurality of washers or deflection discs that bend/deflect under fluid forces experienced during compression. A rebound valve deflection disc stack 210 (also referred to herein as a “rebound valve stack”) sits flush against the entrance openings 204. The rebound valve stack 210 is comprised of a plurality of washers or discs that bend/deflect under fluid forces experienced during rebound. The entrance openings 204 are sized such that the rebound valve stack 210 does not entirely cover the entrance openings 204. By contrast, the compression valve stack 208 may completely cover the exit openings 206.
During the compression phase, fluid flows around the deflection discs of the rebound valve stack 210 and through the entrance openings 204. The pressure of the fluid inside the compression channels 202 pushing against the compression valve stack 208 causes the deflection discs of the compression valve stack 208 to elastically bend, thereby allowing fluid to flow out of the exit openings 206 and into the lower fluid chamber 110. During the rebound phase, the compression valve stack 208 stays closed and prevents fluid in the lower fluid chamber 110 from entering back into the compression channels 202 through the exit openings 206. Rather, rebound channels (not shown in FIG. 2) with entrance and exit openings similar in design are oriented in an opposite direction to allow fluid to flow from the lower fluid chamber 110 to the upper fluid chamber 108 in a relatively similar manner. Such prior art shock absorber offer limited means by which a user can adjust/tune the compression and/or rebound resistance characteristics of the shock absorber.
“External bypass” shock absorbers having external bypass chambers may provide additional means for adjusting rebound and compression resistance characteristics. However, external bypass shock absorbers can be large and unwieldy due to the additional cylinders that lie external to the main shock absorber cylinder. Such shocks may not be appropriate for some applications due space constraints in the wheel well, and/or the cost of additional cylinders and associated material. There exists a need for an internal bypass shock absorber that allows adjustability of the rebound and compression resistance characteristics in a variety of ways, that is also cost effective and not cumbersome.